In an image forming apparatus such as a tandem type multi function peripheral (MFP) or a printer, toner images of plural colors are sequentially superimposed and transferred on a transfer belt or on a sheet transferred by a transfer belt, and a color toner image is formed. And an image forming apparatus a tandem type MFP or a printer, toner images of plural colors are sequentially superimposed and transferred on a transfer belt, and a color toner image is formed. In this tandem type, when the transfer belt meanders, the image quality of the color toner image is remarkably deteriorated by color shift. Thus, hitherto, there are units for correcting the meandering of the transfer belt. As one of such units, for example, Japanese Patent No. 2868879 discloses a belt drive unit in which a steering roller to change the traveling direction of a transfer belt is tilted by using a balance between the elastic force of a spring and the rotation forces of guide rollers at both sides of the steering roller.
However, in the unit of the related art, since the elastic force of the spring is used for the movement of the steering roller, the high-speed property and reliability are insufficient. Thus, it is not appropriate to install the unit in a high-performance and high-speed MFP or the like in which high image quality is required.
Then, the development of a belt transfer device for an image forming apparatus is desired in which when the transfer belt meanders, the transfer belt is returned to a normal direction at high speed, and by this, a high quality color image without color shift can be obtained.